Spherical aberration corrector for electromagnetic lens for charged particle beam

A corrector to be used in combination with an electromagnetic lens for charged particle beam to correct spherical aberration generated by the electromagnetic lens, the corrector comprising:

• an incident plate arranged on an incident side of the charged particle beam;
• and
• an emission plate arranged on an emission side of the charged particle beam,
• wherein
• one of a circular aperture and a ring-shaped aperture is provided on the incident plate,
• another of the circular aperture and the ring-shaped aperture is provided on the emission plate,
• (1) centers of the circular aperture and the ring-shaped aperture are on a center line of the charged particle beam,
• (2) the incident plate and the emission plate intersect perpendicularly to the center line,
• (3) φ3≥φ2>φ1 is satisfied, where a diameter of the circular aperture is φ3, an outer diameter of the ring-shaped aperture is φ2, and an inner diameter of the ring-shaped aperture is φ1,
• (4) when the charged particles are of negative charge, a potential of a plate on which the ring-shaped aperture is provided is higher than a potential of a plate on which the circular aperture is provided, and when the charged particles are of positive charge, the potential of the plate on which the ring-shaped aperture is provided is lower than the potential of the plate on which the circular aperture is provided, and
• an inner portion and an outer portion of the ring-shaped aperture are configured to be electrically conducted.